Re: [Qemu-trivial] [PATCH] RFC kvm irqfd: add directly mapped MSI IRQ support

[Alex Williamson]

On Fri, 2013-06-21 at 11:56 +1000, Alexey Kardashevskiy wrote:
> On 06/21/2013 02:51 AM, Alex Williamson wrote:
> > On Fri, 2013-06-21 at 00:08 +1000, Alexey Kardashevskiy wrote:
> >> At the moment QEMU creates a route for every MSI IRQ.
> >>
> >> Now we are about to add IRQFD support on PPC64-pseries platform.
> >> pSeries already has in-kernel emulated interrupt controller with
> >> 8192 IRQs. Also, pSeries PHB already supports MSIMessage to IRQ
> >> mapping as a part of PAPR requirements for MSI/MSIX guests.
> >> Specifically, the pSeries guest does not touch MSIMessage's at
> >> all, instead it uses rtas_ibm_change_msi and 
> >> rtas_ibm_query_interrupt_source
> >> rtas calls to do the mapping.
> >>
> >> Therefore we do not really need more routing than we got already.
> >> The patch introduces the infrastructure to enable direct IRQ mapping.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> >>
> >> ---
> >>
> >> The patch is raw and ugly indeed, I made it only to demonstrate
> >> the idea and see if it has right to live or not.
> >>
> >> For some reason which I do not really understand (limited GSI numbers?)
> >> the existing code always adds routing and I do not see why we would need 
> >> it.
> > 
> > It's an IOAPIC, a pin gets toggled from the device and an MSI message
> > gets written to the CPU.  So the route allocates and programs the
> > pin->MSI, then we tell it what notifier triggers that pin.
> 
> > On x86 the MSI vector doesn't encode any information about the device
> > sending the MSI, here you seem to be able to figure out the device and
> > vector space number from the address.  Then your pin to MSI is
> > effectively fixed.  So why isn't this just your
> > kvm_irqchip_add_msi_route function?  On pSeries it's a lookup, on x86
> > it's a allocate and program.
> >  What does kvm_irqchip_add_msi_route do on
> > pSeries today?  Thanks,
> 
> 
> As we just started implementing this thing, I commented it out for the
> starter. Once called, it destroys direct mapping in the host kernel and
> everything stops working as routing is not implemented (yet? ever?).

Yay, it's broken, you can rewrite it ;)

> My point here is that MSIMessage to irq translation is made on a PCI domain
> as PAPR (ppc64 server) spec says. The guest never uses MSIMessage, it is
> all in QEMU, the guest dynamically allocates MSI IRQs and it is up to a
> hypeviser (QEMU) to take care of actual MSIMessage for the device.

MSIMessage is what the guest has programmed for the address/data fields,
it's not just a QEMU invention.  From the guest perspective, the device
writes msg.data to msg.address to signal the CPU for the interrupt.

> And the only reason to use MSIMessage in QEMU for us is to support
> msi_notify()/msix_notify() in places like vfio_msi_interrupt(), I have
> added a MSI window for that long time ago which we do not need as much as
> we already have an irq number in vfio_msi_interrupt(), etc.

It seems like you just have another layer of indirection via your
msi_table.  For x86 there's a layer of indirection via the virq virtual
IOAPIC pin.  Seems similar.  Thanks,

Alex

> >> ---
> >>  hw/misc/vfio.c           |   11 +++++++++--
> >>  hw/pci/pci.c             |   13 +++++++++++++
> >>  hw/ppc/spapr_pci.c       |   13 +++++++++++++
> >>  hw/virtio/virtio-pci.c   |   26 ++++++++++++++++++++------
> >>  include/hw/pci/pci.h     |    4 ++++
> >>  include/hw/pci/pci_bus.h |    1 +
> >>  6 files changed, 60 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
> >> index 14aac04..2d9eef7 100644
> >> --- a/hw/misc/vfio.c
> >> +++ b/hw/misc/vfio.c
> >> @@ -639,7 +639,11 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, 
> >> unsigned int nr,
> >>       * Attempt to enable route through KVM irqchip,
> >>       * default to userspace handling if unavailable.
> >>       */
> >> -    vector->virq = msg ? kvm_irqchip_add_msi_route(kvm_state, *msg) : -1;
> >> +
> >> +    vector->virq = msg ? pci_bus_map_msi(vdev->pdev.bus, *msg) : -1;
> >> +    if (vector->virq < 0) {
> >> +        vector->virq = msg ? kvm_irqchip_add_msi_route(kvm_state, *msg) : 
> >> -1;
> >> +    }
> >>      if (vector->virq < 0 ||
> >>          kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
> >>                                         vector->virq) < 0) {
> >> @@ -807,7 +811,10 @@ retry:
> >>           * Attempt to enable route through KVM irqchip,
> >>           * default to userspace handling if unavailable.
> >>           */
> >> -        vector->virq = kvm_irqchip_add_msi_route(kvm_state, msg);
> >> +        vector->virq = pci_bus_map_msi(vdev->pdev.bus, msg);
> >> +        if (vector->virq < 0) {
> >> +            vector->virq = kvm_irqchip_add_msi_route(kvm_state, msg);
> >> +        }
> >>          if (vector->virq < 0 ||
> >>              kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
> >>                                             vector->virq) < 0) {
> >> diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> >> index a976e46..a9875e9 100644
> >> --- a/hw/pci/pci.c
> >> +++ b/hw/pci/pci.c
> >> @@ -1254,6 +1254,19 @@ void pci_device_set_intx_routing_notifier(PCIDevice 
> >> *dev,
> >>      dev->intx_routing_notifier = notifier;
> >>  }
> >>  
> >> +void pci_bus_set_map_msi_fn(PCIBus *bus, pci_map_msi_fn map_msi_fn)
> >> +{
> >> +    bus->map_msi = map_msi_fn;
> >> +}
> >> +
> >> +int pci_bus_map_msi(PCIBus *bus, MSIMessage msg)
> >> +{
> >> +    if (bus->map_msi) {
> >> +        return bus->map_msi(bus, msg);
> >> +    }
> >> +    return -1;
> >> +}
> >> +
> >>  /*
> >>   * PCI-to-PCI bridge specification
> >>   * 9.1: Interrupt routing. Table 9-1
> >> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
> >> index 80408c9..9ef9a29 100644
> >> --- a/hw/ppc/spapr_pci.c
> >> +++ b/hw/ppc/spapr_pci.c
> >> @@ -500,6 +500,18 @@ static void spapr_msi_write(void *opaque, hwaddr addr,
> >>      qemu_irq_pulse(xics_get_qirq(spapr->icp, irq));
> >>  }
> >>  
> >> +static int spapr_msi_get_irq(PCIBus *bus, MSIMessage msg)
> >> +{
> >> +    DeviceState *par = bus->qbus.parent;
> >> +    sPAPRPHBState *sphb = (sPAPRPHBState *) par;
> >> +    unsigned long addr = msg.address - sphb->msi_win_addr;
> >> +    int ndev = addr >> 16;
> >> +    int vec = ((addr & 0xFFFF) >> 2) | msg.data;
> >> +    uint32_t irq = sphb->msi_table[ndev].irq + vec;
> >> +
> >> +    return (int)irq;
> >> +}
> >> +
> >>  static const MemoryRegionOps spapr_msi_ops = {
> >>      /* There is no .read as the read result is undefined by PCI spec */
> >>      .read = NULL,
> >> @@ -664,6 +676,7 @@ static int _spapr_phb_init(SysBusDevice *s)
> >>  
> >>          sphb->lsi_table[i].irq = irq;
> >>      }
> >> +    pci_bus_set_map_msi_fn(bus, spapr_msi_get_irq);
> >>  
> >>      return 0;
> >>  }
> >> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> >> index d309416..587f53e 100644
> >> --- a/hw/virtio/virtio-pci.c
> >> +++ b/hw/virtio/virtio-pci.c
> >> @@ -472,6 +472,8 @@ static unsigned virtio_pci_get_features(DeviceState *d)
> >>      return proxy->host_features;
> >>  }
> >>  
> >> +extern int spapr_msi_get_irq(PCIBus *bus, MSIMessage *msg);
> >> +
> >>  static int kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy,
> >>                                          unsigned int queue_no,
> >>                                          unsigned int vector,
> >> @@ -481,7 +483,10 @@ static int 
> >> kvm_virtio_pci_vq_vector_use(VirtIOPCIProxy *proxy,
> >>      int ret;
> >>  
> >>      if (irqfd->users == 0) {
> >> -        ret = kvm_irqchip_add_msi_route(kvm_state, msg);
> >> +        ret = pci_bus_map_msi(proxy->pci_dev.bus, msg);
> >> +        if (ret < 0) {
> >> +            ret = kvm_irqchip_add_msi_route(kvm_state, msg);
> >> +        }
> >>          if (ret < 0) {
> >>              return ret;
> >>          }
> >> @@ -609,14 +614,23 @@ static int 
> >> virtio_pci_vq_vector_unmask(VirtIOPCIProxy *proxy,
> >>      VirtQueue *vq = virtio_get_queue(proxy->vdev, queue_no);
> >>      EventNotifier *n = virtio_queue_get_guest_notifier(vq);
> >>      VirtIOIRQFD *irqfd;
> >> -    int ret = 0;
> >> +    int ret = 0, tmp;
> >>  
> >>      if (proxy->vector_irqfd) {
> >>          irqfd = &proxy->vector_irqfd[vector];
> >> -        if (irqfd->msg.data != msg.data || irqfd->msg.address != 
> >> msg.address) {
> >> -            ret = kvm_irqchip_update_msi_route(kvm_state, irqfd->virq, 
> >> msg);
> >> -            if (ret < 0) {
> >> -                return ret;
> >> +
> >> +        tmp = pci_bus_map_msi(proxy->pci_dev.bus, msg);
> >> +        if (tmp >= 0) {
> >> +            if (irqfd->virq != tmp) {
> >> +                fprintf(stderr, "FIXME: MSI(-X) vector has changed from 
> >> %X to %x\n",
> >> +                        irqfd->virq, tmp);
> >> +            }
> >> +        } else {
> >> +            if (irqfd->msg.data != msg.data || irqfd->msg.address != 
> >> msg.address) {
> >> +                ret = kvm_irqchip_update_msi_route(kvm_state, 
> >> irqfd->virq, msg);
> >> +                if (ret < 0) {
> >> +                    return ret;
> >> +                }
> >>              }
> >>          }
> >>      }
> >> diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> >> index 8797802..632739a 100644
> >> --- a/include/hw/pci/pci.h
> >> +++ b/include/hw/pci/pci.h
> >> @@ -332,6 +332,7 @@ MemoryRegion *pci_address_space_io(PCIDevice *dev);
> >>  typedef void (*pci_set_irq_fn)(void *opaque, int irq_num, int level);
> >>  typedef int (*pci_map_irq_fn)(PCIDevice *pci_dev, int irq_num);
> >>  typedef PCIINTxRoute (*pci_route_irq_fn)(void *opaque, int pin);
> >> +typedef int (*pci_map_msi_fn)(PCIBus *bus, MSIMessage msg);
> >>  
> >>  typedef enum {
> >>      PCI_HOTPLUG_DISABLED,
> >> @@ -375,6 +376,9 @@ bool pci_intx_route_changed(PCIINTxRoute *old, 
> >> PCIINTxRoute *new);
> >>  void pci_bus_fire_intx_routing_notifier(PCIBus *bus);
> >>  void pci_device_set_intx_routing_notifier(PCIDevice *dev,
> >>                                            PCIINTxRoutingNotifier 
> >> notifier);
> >> +void pci_bus_set_map_msi_fn(PCIBus *bus, pci_map_msi_fn map_msi_fn);
> >> +int pci_bus_map_msi(PCIBus *bus, MSIMessage msg);
> >> +
> >>  void pci_device_reset(PCIDevice *dev);
> >>  void pci_bus_reset(PCIBus *bus);
> >>  
> >> diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
> >> index 66762f6..81efd2b 100644
> >> --- a/include/hw/pci/pci_bus.h
> >> +++ b/include/hw/pci/pci_bus.h
> >> @@ -16,6 +16,7 @@ struct PCIBus {
> >>      pci_set_irq_fn set_irq;
> >>      pci_map_irq_fn map_irq;
> >>      pci_route_irq_fn route_intx_to_irq;
> >> +    pci_map_msi_fn map_msi;
> >>      pci_hotplug_fn hotplug;
> >>      DeviceState *hotplug_qdev;
> >>      void *irq_opaque;
> > 
> > 
> > 
> 
>